There were experiments of radio broadcasting as early as 1905-1906 and commercially as early as 1920-1921. Early radio transmissins only carried dots and dashes of wireless telegraphy. The history of radio broadcasting started with audio that broadcast through air waves from the transmitter to the antenna, then to the device.
Wikipedia states this:
One of the first signals of significant power that carried voice and music was said to have been accomplished in 1906 by Reginald Fessenden when he made a Christmas Eve broadcast to ships at sea from Massachusetts. He played “O Holy Night” on his violin and read passages from the Bible. It should be noted that recent researchers have cast doubt on this story: there is little doubt that Fessenden did ground-breaking experiments with voice and music; however the Christmas Eve broadcast may be a myth. There is considerable evidence that Fessenden demonstrated voice and music long before Christmas Eve 1906. Despite Fessenden’s successful experiments, his financial backers lost interest in the project, leaving others to take the next steps. Early on, the concept of broadcasting was new and unusual—with telegraphs, communication had been one-to-one, not one-to-many. Sending out one-way messages to multiple receivers didn’t seem to have much practical use.
Charles Herrold of San Jose, California sent out broadcasts as early as April 1909 from his Herrold School electronics institute in downtown San Jose, using the identification San Jose Calling, and then a variety of different call signs as the Department of Commerce began to regulate radio. His station was first called FN, then SJN (probably illegally). By 1912, the United States government began requiring radio operators to obtain licenses to send out signals. Herrold received licenses for 6XF and 6XE (a mobile transmitter) in 1916.
He was on the air daily for nearly a decade when World War I interrupted operations. After the war, the Herrold operation in San Jose received the callsign KQW in 1923. Today, the lineage of that continues as KCBS, a CBS-owned station in San Francisco.
Herrold, the son of a farmer who patented a seed spreader, coined the terms broadcasting and narrowcasting, based on the ideas of spreading crop seed far and wide, rather than only in rows. While Herrold never claimed the invention of radio itself, he did claim the invention of broadcasting to a wide audience, through the use of antennas designed to radiate signals in all directions.
By comparison, David Sarnoff has been considered by some, arguably and perhaps mistakenly, as “the prescient prophet of broadcasting who predicted the medium’s rise in 1915”, referring to his radio music box concept.
A few organizations were allowed to keep working on radio during the war. Westinghouse was the most well-known of these. Frank Conrad, a Westinghouse engineer, had been making transmissions from 8XK since 1916 that included music programming.
However, a team at the University of Wisconsin–Madison headed by Professor Earle M. Terry also had permission to be on the air. They operated 9XM, originally licensed by Professor Edward Bennett in 1914, and usually sent Morse code weather reports to ships on the Great Lakes, but they also experimented with voice broadcasts starting in 1917. They reportedly had difficulties with audio distortion, so the next couple of years were spent making transmissions distortion-free.
Following the war, Herrold and other radio pioneers across the country resumed transmissions. The early stations gained new call signs. 8XK became KDKA in 1920. Herrold received a license for KQW in 1921 (later to become KCBS). 9XM became WHA in 1922. And another pioneering station, 8MK in Detroit, Michigan, owned by the Detroit News, became WWJ.
The National Broadcasting Company began regular broadcasting in 1926, with telephone links between New York and other Eastern cities. NBC became the dominant radio network, splitting into Red and Blue networks.
Radio in education began as early as April 1922, when Medford Hillside’s WGI Radio broadcast the first of an on-going series of educational lectures from Tufts College professors. These lectures were described by the press as a sort of “wireless college.” Soon, other colleges across the U.S. began adding radio broadcasting courses to their curricula; some, like the University of Iowa, even provided what today would be known as distance-learning credits. Curry College, first in Boston and then in Milton, Massachusetts, introduced one of the nation’s first broadcasting majors in 1932 when the college teamed up with WLOE in Boston to have students broadcast programs. This success led to numerous radio courses in the curriculum which has taught thousands of radio broadcasters from the 1930s to today.
Prior to 1927, U.S. radio was supervised by the Department of Commerce. Then, the Radio Act of 1927 created the Federal Radio Commission (FRC); in 1934, this agency became known as the Federal Communications Commission (FCC).
A Federal Communications Commission decision in 1939 required NBC to divest itself of its Blue Network. That decision was sustained by the Supreme Court in a 1943 decision, National Broadcasting Co. v. United States, which established the framework that the “scarcity” of radio-frequency meant that broadcasting was subject to greater regulation than other media. This Blue Network network became the American Broadcasting Company (ABC). Around 1946, ABC, NBC, and CBS began regular television broadcasts. Another TV network, the DuMont Television Network, was founded earlier, but was disbanded in 1956.